This invention relates to automatic torque converter transmissions for motor vehicle applications. More particularly, it relates to automatic torque converter transmissions having means to selectively bypass the torque converter and, even more particularly, to a cooling arrangement for a viscous coupling utilized in a torque converter bypass.
Torque converter type automatic transmissions have achieved almost universal application and acceptance in motor vehicles. While generally satisfactory in this application, torque converter automatic transmissions embody inherent slip and, therefore incorporate inherent losses in vehicular fuel economy. In an effort to minimize this slippage and thereby optimize fuel economy, various efforts have been made to bypass the torque converter with some manner of direct drive which is typically brought into play when the vehicle is operating in the highest gear ratio and above a predetermined vehicular speed. While these direct drive bypass arrangements have resulted in improvements in fuel economy, they have also, under certain conditions, served to transmit various drive line vibrations to the passenger compartment of the motor vehicle, resulting in a derogation in the ride quality of the vehicle. In an effort to provide a bypass arrangement that would not transmit drive line vibration to the passenger compartment, it has been proposed that a viscous coupling be employed in the bypass drivetrain. While the use of a viscous coupling in the bypass drivetrain does serve to minimize transmission of drive line vibrations to the passenger compartment, it is imperative that the temperature of the liquid used in the viscous coupling be carefully controlled to avoid deterioration of the liquid with consequent derogation of the performance of the coupling.